不同曲率情况下的液压管道流固耦合特性仿真研究

管道布局影响流体流动特性与管道应力分布。利用有限元方法对不同曲率情况下管道的流固耦合特性进行了分析,研究了流固耦合作用对不同曲率管道位置等效应力的影响。研究结果表明:流体对弯曲管道在弯曲壁面产生额外的作用力导致管道发生变形,且角度的改变会导致两端进出口位置应力发生较大的波动;管道曲率变化对弯管在弯曲附近位置应力影响较大,随着弯曲角度的增加管道弯曲处应力先减小后增大再减小,而内侧和两侧的应力改变幅度不同;管道曲率半径的改变会影响管道的受力分布。通过分析得出管道布局按R30(R/d=1.5)相比其他管道的模型布局更为合理的结论。     

管材参数对输液管流固耦合振动的影响

采用特征线法对一蓄水池-管道-阀门(RPV)系统的流固耦合振动响应进行了数值计算,研究了管道结构阻尼、管材泊松比以及管道壁厚管道材料对系统振动响应的影响。结果表明：随着管道结构阻尼的增大,管壁本身的振动受到抑制;当管道结构阻尼大于某一临界值时,系统的振动能量主要集中在液体里,造成液体压力能的升高;随着泊松比的增大或管道壁厚的增大,液体的压能增大,管壁的轴向振动强度降低。     

舰船低频水下辐射噪声的声固耦合数值计算方法

针对舰船低频域水下辐射噪声计算问题,指出采用严格遵循声固耦合动力学方程的耦合声学有限元与远场自动匹配层(FEM/AML)方法以及耦合声学间接边界元(IBEM)方法是计算精度较高的策略。以某小水线面双体船(SWATH)为研究对象,使用声功率作为评价指标,探讨了声场区域特征尺度选取对计算精度的影响,比较了上述两种方法与常规基于流固耦合的两种方法在计算特性方面的差异。研究表明,声固耦合模式较流固耦合模式声学响应计算结果偏小,对于SWATH船的合成总声功率级两者偏差达到1dB~3dB,前者计算结果更为精确,基于声固耦合模式的耦合声学IBEM方法是舰船水下辐射噪声预报的首选算法。     

基于改进涡方法的膜结构流固耦合研究

采用改进涡方法对膜结构的流固耦合进行模拟。将非协调边界元计算势流的方法引入到传统涡方法中,即为改进涡方法。该算法可以精确计算三维粘性、不可压缩流场。采用改进涡方法可以得到每个时间步膜结构的单元节点流场压力,通过与ansys有限元模型提取出的整体刚度矩阵联合求解得到单元节点位移,并可以由单元节点位移求解出下一时间步的流场分布。由于本文引入了高效的预处理循环型广义极小残余迭代算法(GMRES),使得边界元法的优势得到了充分发挥,大幅度节省了计算时间。完成了方形平屋盖膜结构气弹模型风洞试验。采用本文算法对膜结构流固耦合效应计算得到的位移均值大部分与风洞试验吻合,计算结果表明本文提出的方法是模拟膜结构流固耦合问题的有益尝试。     

强耦合法在膜结构风振流固耦合分析中的程序实现与应用

研究强耦合整体方法在膜结构风振流固耦合效应分析中的程序实现与应用。基于强耦合整体式方程,介绍了采用Fortran语言编写膜结构流固耦合效应计算程序的实现过程,以及程序实现中需要的数值计算方法。对计算程序中的重要求解步骤进行了分析,介绍了相应程序的实现过程。最后将强耦合整体方法计算程序应用于典型膜结构的风振流固耦合计算中,得到了结构在不同风向角下考虑和不考虑耦合效应时的风压系数,其结果与已有风洞试验结果基本一致。同时计算了膜结构的风振响应和周围流场的分布。结果证明提出的强耦合整体方法程序适用于计算膜结构风振中的流固耦合效应,结果正确可靠     

潮流能水轮机单向流固耦合计算方法

基于ANSYS和CFX软件实现了垂直轴潮流能水轮机单向流固耦合瞬态计算。将二维CFX流体计算结果作为水轮机受力,将流体与结构中相对应的节点压力施加到结构有限元模型上,从而完成水轮机工作状态主轴应变计算。将计算结果与实验结果进行对比发现二者吻合较好,说明单向流固耦合方法是将流体计算结果传递到结构分析的有效方法,在潮流能水轮机叶片小变形的条件下能够准确的预报结构响应的趋势,有效的计算垂直轴水轮机的结构强度,对其结构校核起到很好的指导作用     

索膜结构风致流固耦合气动阻尼效应研究

根据三角形重心坐标系原理提出了基于松耦合计算的流固耦合网格协调插值新方法,提高了流固耦合的计算效率;为解决由于柔性结构加速度过大而导致的求解不稳定问题,通过在1个时间步上进行流体及结构间反复交替求解来得到稳定的时程解。应用上述方法对一柔性平屋盖结构进行风振响应的数值模拟计算,通过与风洞试验的对比验证了计算结果的可靠性,并较全面地再现结构在风作用下的实际行为。在此基础上,联合采用经验模态分解法(EMD),随机减量法(RDT)和希尔伯特变换法(HT)从结构的动力响应时程数据中提取到了结构的气动阻尼特性信息。分析结果表明,气动阻尼在柔性结构的风振响应中作用不容忽视,主要表现为:四周封闭建筑的阻尼比远小于迎风面开孔建筑的阻尼比,且四周封闭状态下气动阻尼随风速变化小,其对总阻尼的影响较小;而迎风面开孔状态下气动阻尼较大且随风速的增大而增大。因此,对于柔性且阻尼较小的结构,特别对于开孔结构,气动阻尼的影响不可忽略。     

基于力耦合的非谐振单元组成的超声变幅器设计

传统的超声振动系统全谐振设计方法要求组成超声振动系统的各个单元有相同的谐振频率,各个组成单元的结构尺寸由谐振频率确定,而超声珩齿系统中的齿轮结构尺寸是由它的使用要求决定,是非谐振单元,不能用全谐振理论设计,本文采用力耦合方法,将齿轮简化为环盘,将它和变幅杆组合并联合建立动力学方程,实现了非谐振单元组成的超声变幅器的设计。     

基于PolyMAX的声固耦合模态试验研究

白车身的结构模态频率和模态振型反映了汽车车身结构的固有特性,对车内噪声有重要影响。车内空腔跟车身结构一样,同样拥有模态频率和模态振型。采用LMS数据采集系统对某国产SUV进行车内空腔声学模态试验。首先基于传声器阵列的方法获取响应点的信号,然后利用PolyMAX方法提取声学模态频率及振型。将声学模态频率与白车身结构模态频率进行对比分析,结果表明：车内空腔的第一、二阶声学模态分别跟白车身的第四、十阶结构模态有很强的耦合。最后通过实车测试验证了声固耦合共振时低频轰鸣的存在。可以在关键部件增加板厚、顶盖和地板附加阻尼层、顶盖加加强筋等方式改变车身结构的局部模态来破坏车身结构模态和声腔模态的强耦合状态,降低车内的低频轰鸣声     

高压气井完井管柱系统的轴向流固耦合振动研究

目前针对石油完井管柱的研究没有考虑瞬变流诱发的管柱运动,而实际的管柱与管内流体存在相互影响、相互作用。对完井管柱系统流固耦合振动响应进行了初步分析与探索,给出了适用于气井完井管柱流固耦合分析的数学模型,提供了采用特征线法对耦合模型进行解耦以及采用插值方法进行数值求解的具体过程,并以现场数据为例,预测分析了天然气不稳定流动引起的流体压力、管柱应力、管柱振动速度的耦合响应过程。研究结果表明：天然气不稳定流动使管柱处于交变应力状态,并诱发管柱往复运动,这将加剧完井管柱结构的疲劳破坏与磨损破坏。该结果对预防完井管柱先期实效有实际工程意义     

波谱单元法在空间桁架地震响应分析中的应用

摘 要：针对传统波谱单元法（SEM）只能用于求解节点集中荷载作用下结构动力响应问题的不足,提出了一种通过计算地震等效波谱节点荷载求解桁架结构地震响应的方法。基于虚功原理,利用波谱形函数积分得到地震等效波谱节点荷载的显式表达式,通过修改波谱单元法中单元刚度矩阵的波数,考虑了阻尼对结构动力特征的影响,采用数值拉普拉斯（Laplace）变换替换快速傅立叶（FFT）变换,回避了传统波谱单元法中FFT的周期性问题。利用地震荷载等效后的波谱节点荷载对三维空间桁架结构进行地震响应分析,结果表明,采用本文的方法能方便的计算桁架结构的地震等效波谱节点荷载,精确求解结构的地震响应,与传统有限元法（FEM）相比,大大减少计算单元数量,提高计算精度,且便于编程计算。     

Modelling of unbounded media for fluid-structure interaction applications - a review

Many structures used at sea must be able to withstand the occasional extreme weather conditions and the risk of underwater explosions. This applies not only for military ships and submarines but also for tankers and civil exploration and extraction platforms. An understanding is therefore required of the effects of shock induced water waves and unbounded fluid-structure interaction on floating and submerged structures. For modelling purposes these structures may be considered as a system of five components: the structure itself, any fluid within it, the surrounding fluid including the effects of cavitation, the farfield fluid medium and the effect of shock waves. The first two are sufficiently well understood, the remaining three are the subject of continuous research. Recent developments have created new possibilities for treating the farfield fluid medium. Hence, this paper which discusses the various methods used in the modelling of this problem.     

Polyhedral elements by means of node/edge‐based smoothed finite element method

The node‐based or edge‐based smoothed finite element method is extended to develop polyhedral elements that are allowed to have an arbitrary number of nodes or faces, and so retain a good geometric adaptability. The strain smoothing technique and implicit shape functions based on the linear point interpolation make the element formulation simple and straightforward. The resulting polyhedral elements are free from the excessive zero‐energy modes and yield a robust solution very much insensitive to mesh distortion. Several numerical examples within the framework of linear elasticity demonstrate the accuracy and convergence behavior. The smoothed finite element method‐based polyhedral elements in general yield solutions of better accuracy and faster convergence rate than those of the conventional finite element methods. Copyright © 2016 John Wiley & Sons, Ltd.     

Theoretical aspects of the smoothed finite element method (SFEM)

This paper examines the theoretical bases for the smoothed finite element method (SFEM), which was formulated by incorporating cell‐wise strain smoothing operation into standard compatible finite element method (FEM). The weak form of SFEM can be derived from the Hu–Washizu three‐field variational principle. For elastic problems, it is proved that 1D linear element and 2D linear triangle element in SFEM are identical to their counterparts in FEM, while 2D bilinear quadrilateral elements in SFEM are different from that of FEM: when the number of smoothing cells (SCs) of the elements equals 1, the SFEM solution is proved to be ‘variationally consistent’ and has the same properties with those of FEM using reduced integration; when SC approaches infinity, the SFEM solution will approach the solution of the standard displacement compatible FEM model; when SC is a finite number larger than 1, the SFEM solutions are not ‘variationally consistent’ but ‘energy consistent’, and will change monotonously from the solution of SFEM (SC = 1) to that of SFEM (SC → ∞). It is suggested that there exists an optimal number of SC such that the SFEM solution is closest to the exact solution. The properties of SFEM are confirmed by numerical examples. Copyright © 2006 John Wiley & Sons, Ltd.     

基于有限元的异步电机电磁振动分析

电机的电磁振动是电机电磁场与机械结构耦合的结果,要研究电机的电磁振动,需要将电机的电磁场和结构振动分析结合起来。通过有限元软件,采用一种弱磁-固耦合的方法,对异步电机的电磁振动特性进行分析。首先利用ANSOFT有限元软件建立异步电机的二维有限元模型,计算电机的瞬态电磁场,得到电机在给定转速稳态运行状态下的磁场分布和作用在定子上时变的电磁力;其次用ANSYS有限元软件建立异步电机结构的三维有限元模型,将ANSOFT软件得到的时变电磁力进行频谱分析并校正,然后施加到电机上,计算出电机结构的电磁振动响应。基于对电机电磁振动特性的分析,可以对电机的电磁参数和结构进行改进和优化设计,以降低电机的电磁振动     

水下运动体的三维动力特性分析

在水下运行的物体,由于其与周围水之间的相互作用,从本质来说是一种典型的流固耦合问题。采用位移-压力格式(结构用位移来描述而流体用压力来描述)的流固耦合模型来描述运动体和水之间的相互作用。这种格式和有限元方法将水下运动体的三维动力特性问题,归结为一个大型非对称方程的特征值问题。采用Arnoldi方法进行此非对称特征值的求解。此外,对于刚体模态带来的零频问题,构造出一种特殊的迭代求解格式。最后,给出了一个水下圆柱体的实例计算分析,计算结果表明本文中的方法是切实有效的。     

A spectral stochastic element free Galerkin method for the problems with random material parameter

This paper presents a spectral stochastic element free Galerkin method (SSEFGM) for the problems involving a random material property. The random material property and resulting system response quantity are represented by a probabilistic spectral expansion techniques (Karhunen–Loeve expansion and Polynomical Chaos series, respectively) and implemented into the element free Galerkin (EFG) analysis. Numerical solutions in 1D linear elastic problem with random elastic modulus are introduced, and compared with those of Monte Carlo simulation (MCS) so as to provide the validation of the proposed approach. The present SSEFGM approach can produce a probabilistic density distribution as well as a first‐ and second‐order statistical moments (mean and variance) of response quantity by a single calculation, which is distinguished from an iterative MCS. Moreover, the method is based on an element free analysis so that there is no need of nodal connectivities, which usually require more time and labourious task than main calculations. Thus the proposed SSEFGM approach can provide an alternative analysis tool for the problems contains a stochastic material property, and demands complex mesh structures. Copyright © 2004 John Wiley & Sons, Ltd.     

A truly mesh-distortion-enabled implementation of cell-based smoothed finite element method for incompressible fluid flows with fixed and moving boundaries

Mesh-free properties are part of the superiority of cell-based smoothed finite element method (CS-FEM), but have yet to be fully exploited for computational fluid dynamics. A novel implementation of CS-FEM for incompressible viscous fluid flows in stationary and deforming domains discretized by severely distorted bilinear four-node quadrilateral (Q4) elements is presented in this article. The negative determinant of the Jacobian transformation from the Cartesian coordinates to the natural coordinates is intentionally stipulated for the corresponding mesh over which FEM inevitably fails in practice. It is found that, without ad hoc modifications, CS-FEM incurs unsatisfactory results and even a failure on fixed meshes. To cater for general computations on either a uniform or nonuniform mesh represented by these badly degenerated elements, four smoothing cells (SCs) are deployed in convex Q4 element whereas one SC in concave Q4 element. A simple hourglass control is introduced into those under-integrated quadrilaterals for stabilizing the one-SC quadrature in smoothed Galerkin weak form. Thanks to the adoption of characteristic-based split (CBS) scheme for the fluid solution, a byproduct is the unfolded equivalence of the CBS stabilization and balancing tensor diffusivity under the incompressibility constraint. Several benchmark problems involving incompressible fluid flow and fluid-structure interaction are solved. Numerical results show the good accuracy and robustness of the proposed approach that raises a seductive idea for resolving moving-mesh problems.